Promoting Pore-Level Mass Transport/Reaction In Flow Batteries: Bi Nanodot/Vertically Standing Carbon Nanosheet Composites On Carbon Fibers

Elaborate nanoarchitectured solid/liquid interface design of felt electrodes is arguably the most effective pathway to promote the pore-level transport-reaction processes of redox flow batteries. Herein, we conceive a new type of nanocatalytic-layer-architectured graphite felt via introducing the vertically standing carbon nanosheet-confined Bi nanodots onto carbon fiber surfaces. The vertically standing carbon nanosheets construct a nanoporous layer with straight channels for vanadium ion shuttling, where highly dispersed Bi nanodots are stiffly confined to afford abundant active sites. The vanadium redox flow battery utilizing the rationally designed electrodes achieves an energy efficiency of 89% at 150 mA cm(-2), which is substantially higher than those of raw felt (61%) and oxidized felt (77%). Also, the battery with the present electrode maintains an energy efficiency of over 73% even at 400 mA cm(-2), showing the excellent capability of withstanding fast charging and discharging. The multiphysics simulation shows that the vertically standing architecture optimizes the vanadium ion accessibility to the solid/liquid interfaces and thus maximizes the catalytic activity. Moreover, the battery can sustain more than 1000 cycles without obvious efficiency decay, confirming the superb stability of the present electrode. These encouraging results indicate that engineering vertically standing structures with tailored compositions may open up new avenues for advancing the flow battery technology.